1. Field of the Invention
The present invention relates to communication network apparatus such as is used to link information handling systems or computers of various types and capabilities and to components and methods for data processing in such an apparatus. More particular the present invention relates to schedulers used in such devices to indicate when the next packet is to be transmitted from queues within the devices.
2. Description of the Prior Art
Scheduling the transmission of packets between points within a communications device or between points in the communications device and an external transmission network is well known in the prior art. The conventional approach is to provide a plurality of queues within the device and packets to be transmitted are enqueued to selected queues. A timing device sometimes called a timing wheel or calendar is searched to determine when the next packet is to be dequeued and forwarded from the queues. The selection, queueing and dequeueing of packets are controlled by several factors collectively referred to as Quality of Service (QoS). Because the factors and QoS requirements are well known in the prior art further discussion is not warranted. Suffice it to say U.S. Pat. Nos. 5,533,020 and 6,028,843 are examples of prior art.
Even though the prior art timing devices work well for their intended purpose it is believed that as the number of network users increases and more demand is made for better or higher Quality of Service (QoS) a more practical and efficient timing device will be required.
The requirement that the timing device should be able to support more customers and at the same time provide higher QoS poses a dilemma for the designer. The designer's dilemma is based on the fact that a design that addresses or solves the increased customer problem could adversely affect QoS whereas a design that improves QoS may not necessarily handle a large number of customers.
As a general proposition the increase in customer numbers can be solved by an increase in he number of calendars used in the design. But as the number of calendars increase more time will be required to process the calendars. With QoS time is of the essence. So, as the processing time increases QoS tends to deteriorate. As a consequence the designer is faced with the problems of processing a relatively large number of calendars within a relatively short time interval.
Another problem is that the design should be adaptive to face changing needs of the communication marketplace. If the design is not adaptive whenever conditions, such as addition of customers, change the current design would have to be redone. A more desirable outcome is to have a design which requires minor changes to meet the new requirements. Stated another way the design should be adaptive to accommodate changes.
Many scheduler and associated timing devices are fabricated in solid logic technology. In this technology large number of circuits are fabricated on relatively small areas of silicon termed chip. Space or real estate on the chip is at a premium. As a consequence the designer is allotted a relatively small surface area in which to place the circuits needed to provide the timing function of the scheduler. The requirement to fit the design into the limited space presents another problem for the designer.
In view of the above there is a need to provide an improved timing device to schedule movement of packets within a communications network.